formed in the atmosphere by chemical reaction of anthropogenic or natural gaseous emissions. The major natural emissions of primary particles occur as a result of wind-raised dust and wind-raised sea salt. However, the contribution of particles through gas-to-particle conversion of natural emissions of H2S, N0x, NH3 , and organic compounds may be as great as that from dust and salt. Anthropogenic primary emissions occur from industrial and utility combustion, cement and metals manufacturing, agricultural operations, and several other sources. However, the most important anthropogenic contribution derives from the conversion to sulfates and nitrates of SO2 and N0x emissions. Estimates of the source contributions to atmospheric particles are contained in Table 2.6, which reveals that the anthropogenic contribution to global particle emissions is only about 10% of the total. Mitchell^O estimates a somewhat higher percentage of anthropogenic input (28%) . The major energy inputs to this contribution occur as a result of fly ash from Table 2.6. Estimates of Source Contributions to Atmospheric Particulate Matter
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